Cd-induced phytochelatin synthesis in Dittrichia viscosa (L.) Greuter is determined by the dilution of the culture medium

In this paper, we examined Cd accumulation and PC synthesis in two clones of Dittrichia viscosa, one with a metallicolous (DV-A) and the other with a non-metallicolous origin (DV-W). The clones were cultured in vitro with 0 and 10 mg Cd L⁻¹ in both short-term treatments (up to 72 h) and over 10 days. We also examined the influence of the culture medium dilution and the PC-synthesis inhibitor, L-buthionine-sulfoximine (BSO), on these parameters. Similar Cd accumulation values were found in the two clones. No synthesis of new thiolic compounds was observed in Cd-treated plants cultured in vitro in Murashige and Skoog medium up to 72 h when compared to controls. Dilution of the culture medium affected PC production, increasing it in 1/2 MS and especially in 1/4 MS. Cd uptake did not increase in the same way, but still hyperaccumulation levels were exceeded in all Cd treatments. BSO addition increased the sensitivity of D. viscosa to Cd and diminished Cd accumulation. Nevertheless, a poor correlation between PCs and Cd accumulation capacity was observed since the highest Cd content did not correspond to the highest PC levels. All these results obtained suggest that PCs are important in Cd accumulation and detoxification in D. viscosa and also that other mechanisms might be involved in these traits.